Preheat grill to medium-high heat, about 450°F. Alternatively, preheat your oven to 425°F if baking.
Tear off 4 pieces of heavy-duty aluminum foil, each about 12x12 inches. Lightly spray with non-stick cooking spray.
Divide the steak cubes, shrimp, corn segments, cherry tomatoes, red onion slices, and lemon wedges evenly among the foil sheets.
Season each packet with minced garlic, Old Bay seasoning, thyme, cumin, and black pepper. Drizzle with melted butter for rich flavor.
Fold each foil piece securely to create sealed packets, folding edges tightly to trap steam and flavor.
Place packets directly on the grill or in the oven. Cook for 15 to 20 minutes, flipping once halfway through. Steak should reach an internal temp of 130°F for medium doneness, and shrimp should be pink and opaque.
Carefully open the packets (watch for steam!), sprinkle with fresh parsley, and serve with an extra squeeze of grilled lemon.